Method for sterilizing bulk materials

ABSTRACT

A method and apparatus for sterilizing bulk materials. In the method, sterilization is achieved by means of steam or hot gas. Batches of the material are centrifuged in a closed chamber with simultaneous addition of sterilizing medium. Immediately thereafter, the sterilizing medium is separated out from the material at a sub-atmospheric pressure with centrifuging of the material. The apparatus comprises a pressure-tight container with a builtin centrifuge mechanism. A closed conveyor device is connected to the inlet and outlet of the container, for the supply and discharge of material being handled.

United States Patent Lodige et al. 1 1March 20, 1973 [5 METHOD FORSTERILIZING BULK 1,915,242 6/1933 Rlbelro ..99 215 x MATERIALS 2,086,3387/ 1937 Sodergreen 2,656,988 10 1953 Smith 1 Inventors! Wilhelm g Frillg Josef 2,958,570 11/1960 Fessler Lucke, all of Paderbom, Germany;3,069,734 12/1962 Leuthner Theodor Ernst, Wettingen, Switz 3,088,1795/1963 Leuthner ]and 3,102,781 9/1963 Hoskins et a1.

. 3,164,181 1/1965 Kunz [731 Assignees: Wilhelm Lodige; Fritz Lodige;Josef 3,548,737 12/1970 Evans ..99/216 x STERILE Lucke; by said TheodorErnst, Paderborn, Germany Filed: Feb. 18, 1971 Appl. No.: 116,539

Related US. Application Data Continuation-in-part of Ser. No. 760,803,Sept. 19, 1968, abandoned.

Foreign Application Priority Data Oct. 10, 1967 Germany ..P 16 42 087.4

US. Cl. ..21/56, 21/2, 21/58,

21/93, 21/94, 21/96, 21/98, 99/216 Int. Cl. ..A61l 13/00, A611 1/00Field of Search ..21/56, 93, 2, 91, 92, 9598,

References Cited UNITED STATES PATENTS 8/1932 Anges ..21/91 ux AIR STEAMSTERILE AIR Primary Examiner-Barry S. Richman Attorney-Oberlin, Maky,Donnelly & Renner 5 7] ABSTRACT The apparatus comprises a pressure-tightcontainer with a built-in centrifuge mechanism. A closed conveyor deviceis connected to the inlet and outlet of the container, for the supplyand discharge of material being handled.

6 Claims, 2 Drawing Figures VACUUM i l STEAM STEAM PATENTEUmzmm 3,721,527

SHEET 1 BF 2 VACU U M LIJ i 1 LLl 2 5 INXENTORS a WILHELMHLODIGE, *J,FRITZ LQDIGE,

JOSEF LUCKE ERNST THEODOR STERILE AIR STEAM 1* VACUUM STEAM FIG. 2

. IINVENTORS WILHELM LO'DIGE, FRITZ LGDIGE, JOSEF LUCKE ERNST THEODORMETHOD FOR STERILIZING BULK MATERIALS CROSS-REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of our earlierapplication, Ser. No. 760,803, filed Sept. 19, 1968 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a method ofsterilizing materials by means-of steam, or by means of hot gas. Moreespecially bulk materials such as chips, fibers, powders, foods, feedingstuffs, etc., can be sterilized. The invention is further concerned withapparatus for sterilizing such materials.

In the chemical and pharmaceutical industry, as well as in thefoodstuffs industry, it is often necessary for pulverous or granulatedproducts which are to be processed to be satisfactorily sterile. Steamsterilization is for example suitable for sterilizing such materials.

The steam sterilization of pourable goods has hitherto been carried outin so-called steam autoclaves, saturated steam being supplied to thematerial to be treated, the material being introduced into a chambercapable of being closed in gastight manner. Sterilization then proceedsautomatically in accordance with a preselected time program, but canalso be manually controlled. The charging and emptying of the autoclave,and also the commencement of the program, is in this case effectedmanually by the operating personnel. As a consequence, this knownprocess is only suitable for dealing with very small quantities ofmaterial, the handling of larger quantities being precluded because ofthe necessary manual work with numerous separate operations of thismethod. The charging and emptying of the autoclave could only be carriedout mechanically at heavy expense. In addition, a disadvantage is thatthe autoclave has to be set up in a sterile room if it is desired toprevent the sterilized materials coming into contact with non-sterilesurroundings when the autoclave is emptied. Furthermore, the

sterilization time, depending on the thickness of the bed in theautoclave in which the material to be treated, is long, because thesterilizing medium,such as saturated steam or hot gas, must completelyand sufficiently penetrate through the entire material beforesterilization is completed. Nevertheless, with usual sterilizationtimes, it is never certain that the sterilizing medium acts for asufficiently long time on all parts of the material to be sterilized andthus for the treated batch to have become sterile throughout. Finally,it is also impossible by the known methods to undertake a homogenousconditioning of the sterilized material as regards its temperature andits moisture within a prescribed timetable. A uniform conditioning ishowever of great importance, particularly with foodstuffs and chemicallyactive substances and also with litter or bedding for test animals inresearch laboratories.

An object of the invention is to overcome the aforementioneddisadvantages connected with the known sterilization using saturatedsteam and to provide the possibility of being able to carry out theentire sterilizing operation in a fully automatic manner within anapparatus to be sealed off in sterile form from the exterior and with ashortest possible treatment time. It is also possible, after thesterilization, to add to the material other already sterile substanceswhich do not withstand the high treatment temperatures of steamsterilization.

According to the invention, there is provided a method of sterilizingbulk materials by means of steam or hot gas, wherein the material issterilized batchwise in a closed chamber with centrifuging and withsimultaneous addition of sterilizing medium, and, immediatelythereafter, the sterilizing medium is separatedout from the material ata sub-atmospheric pressure with centrifuging of the bulk material. As aconsequence, it becomes possible for the charging and emptying of thesterilizing apparatus to be effected automatically without theassistance of manual labor. The sterilizing apparatus can withouthesitation be set up in a non-sterile room, since the emptying of theapparatus and of the carrying away of the sterilized material can beeffected in a closed system. Due to the fact that the material to besterilized is loosened, advantageously by the known centrifuging andwhirling method, during the sterilizing operation, the sterilizingmedium can very quickly and uniformly come into contact with all partsof the material, whereby a good sterilizing effect is produced withminimum sterilization times. The same also applies as regards theremoval of the sterilizing medium from the sterilized material after thesterilizing operation has been completed.

In order to accelerate the sterilization, which is carried out.batchwise, the material to be sterilized can be preheated, beforestarting sterilization, by means of relatively small quantities of thesterilizing medium, for example, while the material is introduced intothe sterilization vessel. This medium serving for preheating purposes isthen removed from the sterilizing vessel before starting the sterilizingoperation proper or is even also used for the subsequent sterilization,so that the demand for sterilizing medium becomes correspondinglysmaller.

If the material is sterilized with saturated steam, then drying of thematerial under the action of a vacuum has to be carried out after thesterilizing operation in accordance with a further development of theinvention, the liquid which is still adhering to the material or to theparticles thereof being substantially removed. When sterilizing with hotgas, the gas is likewise extracted by means of a vacuum after completingthe sterilization. Drying is unnecessary in this case, since the hot gashas not supplied any liquid or moisture to the material.

However, if a drying operation is necessary, then in addition externalheat can be supplied to the material while drying. It is at the sametime possible to condition the material while drying, so that itcontains a prescribed moisture content at a specific temperature.Following the drying operation, the sterilized material can in additionbe ventilated with sterile air and then stored in a sterile container.

This method can be carried out in all stages while maintaining aprescribed timing program and in a minimum period of time and producessuperior results.

For carrying out the method as proposed, an apparatus is provided whichcomprises a container which can be closed in pressure-tight manner andwhich is specially adapted for sterilization operations which containerhas a built-in centrifuging mechanism, while a closed transport devicefor supplying and discharging the material being treated is connected tothe inlet and outlet, respectively, of said container. The sterilizingoperation and the drying operation, but at least sterilization and apreliminary drying, can be affected in one and the same container. It isalso possible for the sterilization with the preliminary drying, and thedrying proper, to take place successfully in separate containers.

[n the accompanying drawing,

FIG. 1 is a side elevational view of an apparatus of the invention; and,

FIG. 2 is a transverse sectional view taken on line 2 2 of FIG. 1.

The apparatus comprises a cylindrical container 1, in which thesterilization and also the preliminary drying of the material to betreated is carried out. Mounted longitudinally of the container is ashaft 2 which is driven by a motor 3, preferably at different speedswhich can be selected as desired. The shaft carried centrifuge mechanismto be described hereinbelow for thoroughly loosening and whirling thematerial in the container 1 for sterilization and preliminary dryingpurposes.

The container 1 has a filling mechanism 4 which can be closed inpressure-tight manner, and an inlet pipe 5 of said mechanism has fittedherein a bucket wheel lock chamber 6, which is to prevent the hightreatment temperatures obtaining in the container from being transferredinto the supply device, whereby a fire could easily be caused therein. Apipe conduit can be connected to the inlet side of the said bucket wheellock chamber 6, said pipe providing a connection to a storage vessel forthe material being handled.

Arranged on the top of the container 1 is a dome 7, into which opens avacuum pipe 8 which can be closed off. A closable expansion pipe 9 isalso connected to the dome 7.

Opening into the front end of the container 1 is a pipe 10 for theadmission of sterile air, when a shut-off valve 11 provided in this pipeis opened. A pipe 12 for the supply of the sterilizing medium, such assaturated steam or hot gas, also opens into the container 1.

The complete container 1 is provided with an insulating jacket 13, whichis arranged in the region of the cylindrical container wall at adistance 14 around the container 1. By this means, a double jacket forthe supply of a heating medium is formed. This double jacket is providedwith inlet unions 15 for steam or the like and an outlet union 16 forcondensate, etc., and

contains guide plates (not shown) for guiding the heating medium. It isobviously also possible for a liquid heating medium to flow in thereverse direction through the double jacket.

Arranged on that end wall of the container 1 which is opposite to theinlet end is a closure plug 17 which, when closed, maintains thepressure in the container. The closure plug 17 is opened and closed byan electric motor 18. This closure plug or flap 17 opens into adischarge housing 19, on the top of which is arranged an inspection orcleaning flap 20 which can also serve as a suction union for the mediumused for making the apparatus sterile, which medium is as far aspossible discharged through the pipe 9.

The container 1 is supported on a similarly constructed cylindricaldrying container 21. A centrifuge mechanism to be described is driven bya shaft 22 which is in turn driven by a motor 23 mounted exteriorly ofthe container. An inlet union 24 of the container 21 is connected to theoutlet housing 19 of the container l. The container 21 likewise has adouble jacket 29 with a lower inlet union 30 and an upper outlet union31 for a heating medium, such as hot water. The lower container 21 islikewise provided with an outlet housing 32, which encloses a closureflap or valve 33, which can be opened and closed by an electric motor34. Suitable inlet and discharge lines are provided.

The container 1 is supported by means of feet 25 and 26 on the container21, and the latter in its turn can be supported by feet 27 and 28 on anysuitable support.

Referring to the means for centrifuging the material in the container 1,a plurality of axially spaced, radially extending arms 37 are fixed tothe shaft 2 and carry at the ends thereof mixing tools 35 shapedgenerally in the form of a plow-share. The tools 35 at the opposed endsof the container are transversely truncated to contact the end walls ofthe container. It will be noted that each tool 35 is offset from theaxially adjacent tools, as can also be seen in FIG. 2. Each tool 35 hasa flat, wallengaging, outer edge which functions to scrape and loosenthe material from the walls of the container and to throw the material,due to the shape of the tools, on either side of the tool, therebyenhancing the mixing operation.

It will also be noted that tools 35 are axially offset from each otherthereby serving to facilitate movement of the material from the feed tothe discharge end of the container. The speed of the motor 3 is suchthat the material by centrifugal force is thrown radially outwardlytoward the container walls for scraping action by the tools 35. Thematerial is thereby continuously whirled in the container to enhance thesterilization process.

The container 21 likewise is provided with radial arms 38 at the ends ofwhich are mounted blade-like mixing tools 36. These tools scrape thewalls of the container 21 thereby whirling the material radiallyinwardly. The centrifugal force due to the speed of rotation of theshaft 22 in turn causes the material to be thrown radially outwardly,with the overall effect being to create intensive whirling action of thematerial thereby to enhance the drying operation. Truncated mixing tools39 similar to the endmost tools 35 in the container 1 are provided inthe container 21 to prevent material from being lodged in the corners ofthe container. In addition the mixing tools 36 are pitched relative tothe axis of the shaft 22 to facilitate movement of the material in thecontainer toward the discharge end.

The apparatus described operates in the following manner. The materialto be sterilized is introduced in measured quantities into the container1 from a storage silo, by means of conveyor devices. While the container1 is being filled, a measured quantity of sterilizing medium isintroduced for heating the material and the excess quantity of thisheating medium is withdrawn from the container.

After the completion of the filling operation, the sterilizationcontainer is closed in pressure-tight manner, whereupon saturated steamis introduced into the container for sterilization purposes. Thecentrifuge mechanism provided in the container runs while the containeris being charged and while the sterilizing medium is being introduced.In this way, there is obtained through the mixing tools 35 an intensivewhirling and permeation of the material with the sterilizing medium, sothat the sterilizing operation is completed after a short time, forexample, after 3 minutes. The centrifuge mechanism is then stopped andthe sterilizing medium is released and collected in a suitableinstallation.

By means of a vacuum pipe 8, the sterilizing container l is nowevacuated, in order to dry the material. The centrifuge mechanism startsto run again at a certain reduced pressure, so that all the particles ofthe material participate uniformly in the drying operation, and thus aneffective and uniform drying is produced. The heat necessary for thispurpose is supplied by steam, which flows through the double jacket 14.The material is thereafter ventilated with sterile air and the fullytreated material, after opening the emptying valve 17, is emptied into asterile container, from whence it can be further transported and furtherprocessed.

If the method is carried out in two stages, the sterilized material isdelivered to the container 21 through the unions 19 and 24, and thedrying operation proper and the ventilation with sterile air areeffected in the second container 21.

The evacuation provided during the drying operation can be so controlledthat the centrifuge mechanism is only set in motion when a certainvacuum (e.g. 30 mm. Hg.) is reached, so that none of the material beingtreated passes by suction effect into the vacuum apparatus.

Although the method and apparatus described are primarily for thepurpose of sterilizing bulk materials, it will be apparent to thoseskilled in the art that the apparatus could be used for other purposes,for example, as a polymerization reactor, or wherever intimate mixing isthe desired objective.

We claim:

l. A method of sterilizing bulk materials by means of steam or hot gasin a stationary container defining a closed chamber, comprising thesteps of:

a. introducing said sterilizing medium and said material into saidchamber,

b. subjecting said material to centrifugal force so as to throw thematerial radially outwardly towards the walls of said chamber,

. simultaneously scraping said material from said walls and whirlingsaid material radially inwardly thereby to create an intensive whirlingaction of said material in said chamber to enhance the sterilizationoperation,

(I. evacuating said sterilizing medium from said chamber in the absenceof centrifugal force on said material, and

e. again subjecting said material to centrifugal force at apredetermined, sub-atmospheric pressure while simultaneously scrapingsaid material from the walls of said chamber and whirling said materialradially inwardly thereby to facilitate drying of the sterilizedmaterial.

2. The method of claim 1 further including the step of preheating saidmaterial in said chamber by introducing relatively small quantities ofsaid sterilizing medium into said chamber before the main sterilizingoperation.

3. The method of claim 1 further including the step of ventilating thernaterial, following the drying operatron, with sterile air, and storingsai sterilized ma erial in a sterile container.

4. The method of claim 1 wherein said sterilizing operation is carriedout in a first container and said drying operation in a secondcontainer, and further including the step of transferring saidsterilized material from said first container to said second containerwhile maintaining the pressure existing in said first and secondcontainer.

5. The method of claim 1 further including the step of applying heat tothe exterior walls of said closed chamber during the drying operation.

6. The method of claim 5 further including the step of controlling theapplication of centrifugal force during the drying operation so thatcentrifugal force is applied to said material only when a predeterminedsubatmospheric pressure has been reached.

2. The method of claim 1 further including the step of preheating saidmaterial in said chamber by introducing relatively small quantities ofsaid sterilizing medium into said chamber before the main sterilizingoperation.
 3. The method of claim 1 further including the step ofventilating the material, following the drying operation, with sterileair, and storing said sterilized material in a sterile container.
 4. Themethod of claim 1 wherein said sterilizing operation is carried out in afirst container and said drying operation in a second container, andfurther including the step of transferring said sterilized material fromsaid first container to said second container while maintaining thepressure existing in said first and second container.
 5. The method ofclaim 1 further including the step of applying heat to the exteriorwalls of said closed chamber during the drying operation.
 6. The methodof claim 5 further including the step of controlling the application ofcentrifugal force during the drying operation so that centrifugal forceis applied to said material only when a predetermined sub-atmosphericpressure has been reached.